1. Field of the Invention
This invention relates to perpendicular foils for gas injection into the water flowing close to the moving hull surface.
2. Prior Art
Gas or air injection for drag reduction is typically accomplished by blowing air from screens or ejector slits mounted in the hull surface. To achieve the desired drag reduction requires using a large volume blower and distribution system.
The drag reduction is characterized by the extent the air fills the boundary layer at the moving hull surface. When the air flow is approximately 0.666 the boundary layer flow the maximum drag reduction is achieved. This results in a large amount of gas for achieving adequate coverage of the underwater surface of boats and ships
It is a principal object of this invention to provide floating or submerged hull drag reduction gas injection system using rows of foils set perpendicular to the hull surface with tip gas injection that requires substantially less gas injection than the conventional gas injection system using hull surface screens or ejector slits.
More specifically it is the object to provide rows of foils with tip gas injection by which arranging the foil height corresponding to the local boundary layer thickness will achieve hull drag reduction over a large portion of the hull surface previously economically unattainable with conventional gas injection systems using screens or ejector slits.
Another object is the capability of this system to clean hulls with self-polishing coatings while creating the hull surface drag reduction.
The foregoing objects can be accomplished by utilizing a series of foils with air or gas injection at their tips arranged in rows that project outward from the forward submerged section of a ship or boat hull. Other characteristics of the foils are designated by terms relating to airfoils. Their spans are upright with low to moderate aspect ratio.